1. Field of the Invention
The present invention relates to high speed digital integrated circuits, and in particular, to low voltage differential swing (LVDS) signal drivers for uses in and with high speed digital integrated circuits.
2. Description of the Related Art
With the tremendous growth of the Internet, data transfers, in terms of both volume and speed, are increasing dramatically in all areas of communications. For example, data streams for digitized video signals, high definition television (HDTV) and color graphics data require increasing amounts of bandwidth. As a result, increasingly higher speed interconnects between integrated circuits (chips), functional boards and systems become increasingly critical. While virtually all such data is digital in form, it is a high speed analog circuit technique that has become increasingly prevalent in meeting such data transfer needs. This circuitry, i.e., LVDS, provides for multigigabit data transfers on copper interconnects and high speed transmission lines, including fiber optic applications. These LVDS circuits have proven speed, low power, noise control and cost advantages important in point-to-point applications for telecommunications, data communications and video displays.
However, while LVDS circuits continue to provide significant advantages in applications requiring high data transfer rates, such circuits are not immune from three major parameters that influence the operation of virtually any circuit or system: circuit fabrication (or manufacture) process variations (xe2x80x9cPxe2x80x9d); power supply voltage variations (xe2x80x9cVxe2x80x9d); and operating temperature variations (xe2x80x9cTxe2x80x9d); often referred to collectively as PVT.
With respect to fabrication process variations, it is well known that notwithstanding the stringent quality control measures typically used to fabricate integrated circuits, fabrication processes nonetheless suffer some variations among the various processing parameters.
With respect to power supply variations, it is well known that notwithstanding the use of various filters or shielding techniques, noise and especially low frequency noise can be present or induced in the power supply line (e.g, switching noise, electromagnetic interference, etc.). Power supply noise can cause jitter on the rising and falling edges of the signal being processed, as well as frequency skew within the output signal.
With respect to operating temperature variations, such variations will virtually never be avoidable, as operating temperatures can vary due to a number of causes, including variations in data transfer rates, ambient temperature, variations in power supply voltage, among others. As operating temperatures vary, so can the amplitude, phase and frequency of some of the signals being processed.
A low voltage differential swing (LVDS) signal driver in accordance with the presently claimed invention maintains a constant output differential voltage (Vod) over variations in circuit fabrication processes, power supply voltages and operating temperatures (PVT). The minimum and maximum values of the LVDS output signal are monitored and, based upon the difference between them, a signal is provided to the LVDS circuit to control the LVDS output signal such that its peak-to-peak value is maintained at a predetermined value.
In accordance with one embodiment of the presently claimed invention, a low voltage differential swing (LVDS) signal driver includes differential signal driver circuitry and feedback circuitry. The differential signal driver circuitry receives a control signal and in response thereto receives and converts a dual differential input signal to a LVDS signal having minimum and maximum values. The feedback circuitry, coupled to the differential signal driver circuitry, receives the LVDS signal and in response thereto provides the control signal, wherein a difference between the minimum and maximum LVDS signal values is maintained at a predetermined value.
In accordance with another embodiment of the presently claimed invention, a low voltage differential swing (LVDS) signal driver includes signal driver means and feedback means. The signal driver means is for receiving a control signal and in response thereto receiving and converting a dual differential input signal to a LVDS signal having minimum and maximum values. The feedback means is for receiving the LVDS signal and in response thereto providing the control signal and maintaining a difference between the minimum and maximum LVDS signal values at a predetermined value.
In accordance with still another embodiment of the presently claimed invention, a method for generating a low voltage differential swing (LVDS) signal driver includes:
receiving a control signal;
receiving a dual differential input signal;
converting the dual differential input signal to a LVDS signal having minimum and maximum values in response to the control signal; and
generating the control signal in response to the LVDS signal and thereby maintaining a difference between the minimum and maximum LVDS signal values at a predetermined value.